Note Out of dozens of samples there were 4 diagnosed with Cytospora canker by the OSU Plant Clinic. Other pathogens associated with cankers in other samples included Fusarium and Nectria as well as bacterial canker.
Cankers can cause poor tree growth and may not be on all branches.
Photo from Dr. Krishna Mohan, ISU.
A cut from a pocket knife reveals that under the canker the vascular cambium is brown and necrotic rather than light green.
Necrotic tissue, due to Tomato ringspot virus, at the exposed graft line between a 'Golden Delicious' scion and a 'M1-106' rootstock.
Photo by Iain MacSwann, 1977
Cause Tomato ringspot virus is spread by dagger nematodes, Xiphinema americanum (sensu lato). The virus occurs in many areas of Eastern North America, and has been reported occasionally in the Pacific Northwest and California. The host range of the virus is wide including many fruit, ornamental, and vegetable crops as well as many weeds.
The bark has been removed from this Red Delicious apple tree to expose the graft union. Note the line of damaged tissue between the rootstock and scion.
Cause These diseases are caused by apple scar skin viroid. Many infected cultivars of apple or pear do not express symptoms of disease. It has become a problem when old orchards are top worked, and the new scion is susceptible to the viroid that had been symptomless in the original cultivar. Pear also appears to be a symptomless carrier of apple scar skin viroid. The pathogen occasionally spreads slowly in the orchard, but the mechanism(s) is not known as there is no known insect vector.
Scab lesions can distort the growth of the fruit as can be seen between the healthy on the left and the diseased on the right.
Photo part of the OSU Extension Plant Pathology Slide collection
Tree on the left was treated with fungicide while the tree on the right was nontreated. Note the thin canopy and defoliation of the tree on the right.
Jay W. Pscheidt, 2010.
Scab lesions can occur on either side of the leaf. Leaf on top shows lesion on the lower leaf surface.
Jay W. Pscheidt, 2017.
Scab lesions distort apples and can cause them to split open and rot from other organisms.
OSU Plant Clinic Collection.
Scab lesions can be subtle as with the lighter green areas on this leaf. The brown necrotic spots are not scab lesions (see necrotic leaf spot section).
Jay W. Pscheidt, 2012.
Numerous scab lesions on this apple.
Photo by Bob Spotts, 1982
Note the olive-brown lesions on this apple leaf. Apple scab (Venturia inequalis)
